1. Field of the Invention
The present invention relates to an integrated Power Factor Correction (PFC) and Pulse Width Modulation (PWM) controller, and more specifically to an integrated PFC and PWM controller with a plurality of frequency-load curves to make a Power Supply Unit (PSU) more energy-efficient, i.e. to minimize the no-load power consumption and maximize 4-point average efficiencies. Each frequency-load curve has four operating modes: Holdup Mode (HM), Burst Mode (BM), Discontinuous Conduction Mode (DCM), and Continuous Conduction Mode (CCM). The disclosed controller selects a frequency-load curve among the plurality of frequency-load curves and controls the PFC stage and the PWM stage to operate in HM, BM, DCM, or CCM based on the combined result from the input voltage and the output load sense signals, fetched respectively from the input terminal of the PFC stage and the output terminal of the PWM stage. More specifically, the disclosed controller, which can be realized in any shape or form, be it analog or digital; discrete or integrated, would have the PSU operate in HM in case of no load, in BM in case of little load, in DCM in case of light load, or in CCM in case of heavy load across the flyback output rail. In other words, the integrated controller controls the PSU to operate in BM, DCM and CCM as the load increases.
2. The Prior Arts
Causing the AC input current to be in phase with the AC input voltage from the AC mains, a resistor consumes real power. On the contrary, an inductor or a capacitor stores and releases imaginary power from and to the AC mains because of causing the AC input current to be in quadrature with the AC input voltage. Simply put, a resistive load only consumes real power while an inductive or capacitive load not only consumes real power but also stores and releases imaginary power.
The imaginary power, flowing back and forth between the AC mains and the AC load, leads to an increased power line loss power companies wouldn't take lying down. Therefore, power companies strongly request that the Power Factor (PF) of large electrical or electronic devices be strictly corrected to an acceptable value to get rid of unnecessary burden and waste. The higher the PF, the less the imaginary power and the less the power line loss.
Generally speaking, to correct the PF is to align the AC input current to be in phase with the AC input voltage. When it comes to switch-mode power supplies, a PWM stage whose AC input power exceeds 75 W and whose AC input current is far from being sinusoidal should be preceded by a PFC stage to keep the AC input current both in phase and in shape with the AC input voltage so that the combination of the PFC stage and the PWM stage would take in a quasi-sinusoidal AC current just like a resistor with unity PF.
In prior arts where 90˜150 W power adapters are of primary interest, the PFC stage is generally implemented/realized with a Discontinuous Conduction Mode (DCM) PFC, a Boundary Conduction Mode (BCM) PFC, or a Continuous Conduction Mode (CCM) PFC and the PWM stage with a Single-Switch Quasi-Resonant (SS-QR) flyback converter or a Dual-Switch Quasi-Resonant (DS-QR) flyback converter, depending on the power demand. A world of integrated PFC and PWM controllers has also been developed for each of all 3*2=6 possible combinations of the PFC stage and the PWM stage.
Those traditional integrated PFC and PWM controllers can perform up to par, but the problem is that they are all limited to having a single frequency-load curve, making the minimization of the no-load power consumption or the maximization of 4-point average efficiencies a difficult job for PSU designers.
In view of this deficiency of traditional integrated PFC and PWM controllers, the present invention left no stone unturned in search of no-load power consumption minimization and 4-point average efficiencies maximization and came up with an integrated PFC and PWM controller with a plurality of frequency-load curves to do the trick.